Various types of dot matrix line printers have been proposed and are in use. In general, dot matrix line printers include a plurality of dot forming components having their dot printing elements lying along a line that is orthogonal to the direction of paper movement through the printer. Since paper movement is normally vertical, the dot printing elements usually lie along a horizontal line. Located on the side of the paper remote from the dot forming elements is a platen; and, located between the dot forming elements and the paper is a ribbon. During printing, the dot forming elements are oscillated back and forth along the horizontal line that they define. At predetermined positions, as required by the image or characters to be formed, selected ones of the dot forming elements are actuated to press the ribbon against the paper and, thus, create dots. A series of thusly formed dot rows creates a row of characters. The paper, of course, is incremented between the formation of the dot rows. While the present invention was developed for use in dot matrix line printers to shuttle or oscillate the dot forming elements and, thus, finds its primary use in this area, it is to be understood that the invention can be used to shuttle carriages of other mechanisms, including other types of printer mechanisms.
In general, dot matrix line printers fall into two categories. In the first category are dot matrix line printers wherein only the dot forming elements are oscillated back and forth along the horizontal line that they define. In the second category are dot matrix line printers wherein the actuating mechanism, as well as the dot forming elements, are oscillated. Regardless of the type, the portion of the printing mechanism to be oscillated is mounted on a carriage; and, the carriage is oscillated by a shuttling mechanism. Since the present invention is directed to carriage shuttling mechanisms, it is suitable for use in both categories of dot matrix line printers.
In the past, various types of carriage shuttling mechanisms have been proposed for use in dot matrix line printers. One type of carriage shuttling mechanism includes a stepping motor that is actuated to cause step increments of carriage movement. After each step, the appropriate actuators are energized to create dots. Bi-directional movement is provided by stepping the carriage first in one direction, and then in the opposite direction.
One major problem attendant to the use of stepping motors in dot matrix line printers is the speed limitations that they place on the rate of printing. That is, a step-print-step-print-step-print etc. sequence is slow compared to a system wherein carriage movement is continuous and printing occurs "on-the-fly". As a result, proposals have been made to provide constant speed carriage movement mechanisms. Such proposals have included the use of constant speed motors and voice coil types of linear motors. One of the problems with the use of constant speed motors is the limitations placed on the mechanisms used to couple the shaft of the constant speed motors to the printer carriage. The major limitation is the desirable requirement for constant carriage velocity over the print area. Examples of mechanisms that meet this limitation are described in U.S. patent application Ser. No. 169,595 entitled, "Bi-directional, Constant Velocity Carriage Shuttling Mechanisms", by Edward D. Bringhurst et al. filed July 17, 1980. In the mechanisms described in this patent application, a constant speed DC motor rotates a first bi-lobed second order elliptical gear. The first bi-lobed second order elliptical gear is connected directly (or indirectly, i.e., via a belt) to a second identically sized bi-lobed second order elliptical gear. The second bi-lobed gear is eccentrically linked to the carriage to be shuttled. While such mechanisms are suitable for use in shuttling the carriage of a dot matrix line printer they have the disadvantage of requiring precisely formed, uniquely shaped gears. Such gears are expensive to produce as well as being subject to wear. Also, such gears are undesirably bulky.
While voice coil type linear motors have a number of advantages over the use of stepping motors, they also have a number of disadvantages. For example, voice coil type linear motors are relatively expensive and, more bulky than desirable. Moreover, voice coil type linear motors are more sensitive to alignment during the assembly of the overall carriage shuttling mechanism than is desirable.
Thus, it is an object of this invention to provide a new and improved rotary-to-linear motion conversion mechanism.
It is a further object of this invention to provide a rotary-to-linear motion conversion mechanism that is particularly suited for use in a dot matrix line printer.
It is a still further object of this invention to provide an inexpensive, small size shuttling mechanism for dot matrix line printers.